Helium recovery

ABSTRACT

A gas recovery system comprising a source of gas having a preselected concentration of a desired component ( 9 ), at least one application ( 1 ) that adds impurities to said gas, and at least one an adsorption system ( 6 ) that purifies said gas to produce a purified gas for re-use in application ( 1 ), wherein said at least one adsorption system includes at least one adsorbent bed (A) having at least three layers of adsorbents. A recovery process is also disclosed.

FIELD OF THE INVENTION

[0001] The invention relates to the recycle and purification of heliumgas streams for industrial applications.

BACKGROUND OF THE INVENTION

[0002] Gases such as helium, argon, neon, krypton and xenon have thepotential to be used in a wide range of manufacturing processes. Anexample of one such process is the production of semiconductor devicessuch as semiconductor integrated circuits, active matrix liquid crystalpanels, solar cells panels and magnetic discs. During the manufacture ofthe semiconductor devices, systems for generating plasma in a noble gasatmosphere under reduced pressure are utilized for various treatments ofthe semiconductor devices with the plasma, for example, a sputteringsystem, a plasma CVD system and reactive ion etching system. Inaddition, noble gases are used in other applications such as metalatomization processes, cold spray forming, cooling, and shield gasapplications.

[0003] Most of the aforementioned applications use large quantities ofnoble gas such as helium. The cost of using helium would be prohibitivewithout some form of recycle system for the used gas. In order torecycle the noble gas to the application, impurities such as water,nitrogen, oxygen, carbon dioxide, methane carbon monoxide, hydrogen andparticulates from furnace off gas must be removed from the used gas.

[0004] Various purification systems have been proposed in the prior art.Such systems include helium recycle with membrane, thermal swingadsorption (TSA), pressure swing adsorption (PSA) and/or copper oxidetechnology. The choice of purification technology depends on the type ofprocess, the off-gas impurities and inlet feed gas compositions. Forexample, if the only contaminant in the noble gas is oxygen, then acopper oxide getter could be used to take out oxygen. However, if onlywater is present, then a dryer operating in TSA mode may be used. Ifboth water and oxygen are present, then a combination of copper oxidegetter and dryer may be used for purifying the noble gas (e.g., helium).

[0005] Ohmi et al., in U.S. Pat. No. 6,217,633 B1 discloses a processand an apparatus for recovering a noble gas (defined as one or more ofXe, Ar, Kr Ne or mixtures thereof) contained in an exhaust gas from anoble gas employing unit. In particular, the invention of Ohmi et al.,provides a process an apparatus for recovering a noble gas at highrecovery and predetermined purity from a noble gas employing system suchas plasma treating system. The noble gas employing system operates underreduced pressure. The recovery unit receives intermittent feed gas basedon the impurity concentrations in the used gas (exhaust gas) leaving thenoble gas employing unit. The impurities include oxygen, nitrogen,water, carbon monoxide, carbon dioxide, carbon fluoride, hydrogen andvarious film-forming gases. If the impurity concentrations are beyondcertain limits, then the used gas is exhausted as waste instead of beingsent to the recovery unit. The choice of venting exhaust gas from thenoble gas employing system as waste or sending to the recovery unitdepends on the content of impurity components contained in the exhaustgas or on the running state of the noble gas employing system.

[0006] U.S. Pat. No. 5,390,533 describes a process for pressurizing avessel for integrity testing using helium as the tracer gas. Theinvention also discloses the recovery and purification of helium forreuse. The process for purifying the gas stream comprises drying the gasstream using a membrane dryer that permeates water. The water depletedraffinate from the membrane dryer is sent to a membrane separator forfurther purification. Helium selectively permeates the membrane in themembrane separator to produce a helium enriched permeate stream. Thehelium-depleted raffinate stream is sent to a membrane stripper stage toobtain a purge stream to purge water from the membrane dryer.

[0007] Behling et al., in U.S. Pat. No. 6,179,900 B1 disclose processesfor the separation/recovery of gases where the desired component to beseparated from the mixture is present in low molar concentrations and/orlow to moderate pressures. A combined membrane/PSA process is utilizedfor the separation/recovery of gaseous components which are present inthe stream at low pressures and/or molar contents. The membrane unit ispositioned at the upstream end of the PSA process.

[0008] U.S. Pat. No. 6,902,391 discloses helium recycling for opticalfiber manufacturing in which consolidation process helium is recycledeither directly for use in consolidation at high purity or recycled atlower purity for usage in draw or other processes requiring lower heliumpurity. In addition, integrated processes for recycling helium from twoor more helium using processes in the optical manufacturing process arealso disclosed. U.S. Pat. No. 5,707,425 to D'Amico et al., describes aprocess that is directed to the recovery of helium gas from gas streamscontaining about 25% by volume or more of helium. Two PSA processes areused in a serial arrangement. Stoner et al. in U.S. Pat. No. 5,632,803discloses a hybrid membrane/PSA process for producing a helium productstream at a purity in excess of 98.0% from feed stock containinganywhere from 0.5 to 5.0% helium. The membrane is placed upstream of twoPSA processes, and all of the separation units are arranged in a serialconfiguration.

[0009] U.S. Pat. No. 5,377,491 describes a coolant recovery process fora fiber optic cooling tube. The process uses a vacuum pump/compressor toremove cooling gas from the cooling tube, remove particulate andcontaminants and then return the coolant gas to the fiber optic coolingtube. Purification equipment such as PSA, dryer and membrane arementioned for the removal of water and oxygen.

[0010] U.S. Pat. No. 5,158,625 discloses a process for heat treatingarticles by hardening them in a recirculating gas medium which is incontact with the treated articles. According to one of the embodiments,used helium is collected and sent to a membrane unit to produce purifiedhelium at low pressure. The purified helium from the membrane unit issent to a dryer prior to reuse. In another embodiment, theused/contaminated helium is mechanically filtered, then oxygen isremoved via controlled addition of hydrogen for catalytic production ofwater, after which the gas is possibly cooled and dried for reuse. Inanother embodiment, hydrogen is used for regenerating a catalyst usedfor trapping oxygen. Also, in a further embodiment, PSA or TSA is usefor removing oxygen and water vapor, after which the gas is cooled anddried. Knoblauch et al., U.S. Pat. Nos. 5,089,048 & 5,080,694 disclosePSA processes, arranged in a serial configuration, for extracting heliumfrom a relatively helium poor gas mixture, e.g., natural gas containing2-10% helium. The first PSA process is used for helium enrichment andthe second PSA process is used to achieve target helium purity of atleast 99.9%.

[0011] Choe et al., in U.S. Pat. No. 4,717,407 discloses a heliumrecovery system by integrating permeable membrane separation with“non-membrane” separation techniques. The patent refers to PSAapplications as one of the possible “non-membrane” separationoperations. Czarnecki et al., U.S. Pat. No. 4,675,030, disclose a methodof purifying helium gas contaminated with air, water vapor and traces ofcarbon dioxide. The contaminants constitute less than about 10% byvolume. According to this invention, the process contaminated helium gasis compressed and cooled to condense the bulk of the water vapour thenthe dried gas is passed to a first membrane unit to produce high purityhelium for reuse. The retentate from the first membrane unit is passedto a second membrane unit. The permeate of the second membrane unit isrecycled back to the first membrane unit, whereas, the retentate of thesecond membrane unit is discarded as waste.

[0012] U.S. Pat. No. 4,238,204 outlines an improved selective adsorptionprocess for the recovery of a light gas, such as hydrogen or helium,from a feed gas mixture by utilizing a membrane permeator unitselectively permeable to the light gas being collected. Specifically,this invention utilizes a hybrid PSA/membrane process to recover helium.The PSA process is placed upstream of the membrane unit, and theeffluent of the PSA process during the adsorption is collected asproduct helium. The exhaust gas from the PSA process, obtained duringthe purging step, is sent to a membrane unit for additional furtherpurification. The permeate from the membrane unit is recycle to the PSAfeed. The non-permeated gas mixture comprised mainly of the impuritiesand a small proportion of the helium is recovered for other use ordisposed of as waste.

[0013] The prior art processes suffer from low helium purity and perpass recovery when using a single stage PSA process alone to recoverhelium. In addition, in order to achieve enhanced helium purity andrecovery, the prior art typically utilized a combination of PSA andmembranes, or PSA and cryogenic systems, or serial arrangements of PSAprocesses using different number of beds and PSA cycles. Consequently,using the prior art, the capital and operating costs are too high topromote the use of recovery systems to conserve noble gas such ashelium.

OBJECTS OF THE INVENTION

[0014] It is therfore an object of this invention to provide a highlyefficient and low cost noble gas (e.g., helium) recovery system topurify helium from one or more feed sources (e.g., metal atomizationfurnaces, plasma-arc furnaces, natural gas, etc.)

[0015] It is another object of this invention to provide a heliumrecovery system that will remove contaminants such as O₂, N₂, H₂O, CO,CO₂, H₂, metals, and metal salts from spent helium exiting from variousapplications (e.g., atomization furnaces).

[0016] It is a further objective to provide a helium recovery process torecover and purify helium for use in semiconductor applications.

SUMMARY OF THE INVENTION

[0017] The present invention is a highly efficient and low cost noblegas (e.g., helium) recovery system for the recovery and conservation ofnoble gas (e.g., helium) used in various applications. The recoverysystem may be used for noble gas recovery from any application usingnoble gas including but not limited to atomization furnaces, metalatomization, plasma CVD, sputtering system, reactive ion etching system,and plasma-arc furnaces.

[0018] The recovery process uses a PSA process with adsorbents havingthe capability to remove contaminants such as O₂, N₂, H₂O, CO₂, and CO.

[0019] In one embodiment, the invention comprises a gas recovery systemcomprising a source of gas having a preselected concentration of adesired component (e.g. a noble gas), at least one application that usessaid gas and adds impurities to said gas, and at least one an adsorptionsystem that purifies said gas to produce a purified gas for re-use inapplication, wherein said at least one adsorption system includes atleast one adsorbent bed (A) having at least three layers of adsorbents.

[0020] In a more preferred embodiment, the desired component is helium,and said preselected concentration is 99.999 mole %

[0021] In an alternative embodiment, a gas recovery process is alsodisclosed, the process comprising the steps of

[0022] a) providing gas having a preselected concentration of a desiredcomponent to an application,

[0023] b) adding impurities to said gas in said application to producean impure gab having a lower concentration of said desired component;

[0024] c) passing said impure gas to an adsorption system that purifiessaid gas to produce a purified gas (preferably having having saidpreselected concentration of said desired component) for re-use inapplication, wherein said adsorption system includes at least oneadsorbent bed (A) having at least three layers of adsorbents.

[0025] In a preferred embodiment, the waste gas produced from adsorptionsystem (which has a second concentration of said desired component whichis lower than said preselected concentration), is recirculated throughsaid adsorption system for purification to produce a purifiedrecirculated gas having a concentration of the desired component that ispreferably at least as high as said preselected concentration, which maythen be provided to said application.

[0026] In another embodiment of the process, the adsorption system wastegas is directed to a membrane system (7) which produces a partiallypurified gas having a higher concentration of said desired componentthan said waste gas, and wherein said partially purified gas is combinedwith said impure gas which is then passed through said adsorption systemfor purification.

BRIEF DESCRIPTION OF THE DRAWING(S)

[0027] Other objects, features and advantages will occur to thoseskilled in the art from the following description of (a) preferredembodiment(s) and the accompanying drawing(s), in which:

[0028]FIG. 1 is a process flow diagram of an embodiment of the inventionutilizing a hydrogen removal unit, PSA system and membrane unit.

[0029]FIG. 2 schematic diagram showing a layered adsorbent bed inaccordance with the invention.

[0030]FIG. 3 shows adsorption isotherms of water on activated carbon(AC), 5A zeolite and alumina at 300K.

[0031]FIG. 4 shows adsorption isotherms of CO₂, CH₄, CO, N₂ and H₂ onalumina at 300K.

[0032]FIG. 5 shows adsorption isotherms of of CO₂, CH₄, CO, N₂ and H₂ onactivated carbon (AC) at 300K.

[0033]FIG. 6 shows adsorption isotherms of nitrogen on CaX, LiX, 5A,VSA6 and H-15 zeolites at 300K.

[0034]FIG. 7 shows adsorption isotherms of oxygen and argon on oxygenequilibrium selective adsorbent (IA-3) at 300K.

[0035]FIG. 8 is a process flow diagram for a PSA system used in theinvention.

[0036]FIG. 9 is a process flow diagram in accordance with an embodimentof the invention showing.

[0037]FIG. 10 is a process flow diagram in accordance with an embodimentof the invention showing two applications in combination with tworecovery systems.

DETAILED DESCRIPTION OF THE INVENTION

[0038] The invention provides a method for decreasing the impurities ina product gas from a PSA process for separating helium from impuritiesincluding O₂, N₂, H₂O, CO₂, CH₄, and CO.

[0039]FIG. 1 shows one embodiment of a helium recovery system from anapplication 1 using helium gas. High purity helium gas (e.g. 99.999% He)for start up and make-up (for gas lost during recycle process) isprovided from storage tank 9. Via lines 9 a and 9 b respectively it isdirected via product ballast tank 8 to the application requiringpurified helium.

[0040] Optional Vacuum pump 3 is used to pull gas from the applicationunit 1 after it is collected and cooled in an optional aftercooler 2. Ifthe gas coming out of the application 1 is under positive pressurevacuum pump 3 is not required. The gas is compressed in recyclecompressor 4, heated, then passed to the recovery system which purifieshelium for recycling. The compressor 4 can be one of a number ofdesigns. However, if streams containing particulates are involved thenliquid ring compressors may be preferred. The recovery system/processincludes the use of PSA system 6, with optional hydrogen removal unit 5(if required), and optional membrane unit 7.

[0041] The optional hydrogen removal unit 5 converts hydrogen and oxygento water over a catalyst, typically a palladium catalyst. Other catalystmaterials are well known to those skilled in the art. A honeycombmonolith is used as the substrate for the palladium catalyst in thehydrogen removal unit. The catalyst chamber may be flanged slightly offcenter in order to facilitate removal of the monolith easily to wash offcontaminants with soap and water. The hydrogen-deficient gas is thencooled and any condensed water removed via an optional separator orcoalescing filter (not shown). It is then compressed to a desiredpressure and sent to the PSA system 6 for removal of contaminants suchas H₂O, CO₂, N₂, O₂, CH₄ and CO. The purified gas from the adsorptionsystem is then stored in product ballast tank 8 and recycled to thehelium application unit(s) 1.

[0042] Waste gas containing helium and impurities flows out of the PSAunit 6 during the regeneration step and, if desired, is passed through amembrane unit 7 where helium is selectively permeated to produce ahelium enriched gas stream which is directed to the suction side of therecycle compressor 4. Helium depleted raffinate from the membrane isdiscarded via conduit 12. An optional bypass loop may be engaged whichbypasses the application 1. In this case flow to the application wouldbe terminated and redirected to conduit 13 such that PSA product gas isrecycled directly to ensure proper operation of the recycle system. Inthe event the PSA waste gas is not passed through the membrane, this gasmay be recirculated through the PSA via compressor 4. Waste gas may alsosimply be vented via conduit 11 (at the cost of reduced productrecovery)

[0043] Upstream of the optional membrane unit 7 an optional surge tank10 may be used to smooth out oscillations of the PSA waste gas to themembrane unit. A portion of the helium containing waste gas entering thesurge tank (upstream of the membrane) may be vented via conduit 11 tobalance the amount of impurities in the total system with the impuritiescoming from the furnace.

[0044] Since the waste gas from the PSA system 6 goes through the surgetank 10, then the membrane 7, then back to the suction side of thecompressor 4, the PSA will concentrate the impurities from 10 to 10,000times greater than what they were when they came out of the application1. (e.g. if the application reduces the purity of He gas from 99.999mole % down to 99.0 mole %, the PSA can purify the contaminated gas toproduce product gas of 99.999 mole % He). Thus, the amount of heliumdiscarded in the inventive process is relatively small, and high heliumrecovery (e.g. greater than 90%, preferably greater than 95%)_ isachieved.

[0045] The PSA system 6 uses a pressure swing adsorption process topurify the contaminated helium feed gas to produce a high purityproduct. The impurities are adsorbed from the feed gas at the feed gaspressure and then desorbed at a lower pressure.

[0046] The preferred adsorption process uses four adsorber beds (A-D)and provides a continuous product flow. The process operates on arepeated cycle having two basic steps comprising adsorption andregeneration. During a preferred cycle, one vessel is always adsorbingwhile the others are in various stages of regeneration. During theadsorption step, impurities are adsorbed by the adsorbent, thusproducing a high-purity product. During the regeneration step, theimpurities are cleaned from the adsorbent so that the cycle(adsorption/regeneration) can be repeated.

[0047] The exhaust/waste gas from the PSA 6, obtained during theregeneration of the PSA beds, may be sent to the membrane unit 7 forbulk impurities removal and to improve recovery as described above. Thusthe feed to the recycle system consists of the used helium gas from theapplication unit and the enriched helium membrane recycle gas, and/or insome cases (where no membrane is used) waste gas from the PSA.

[0048] While a four bed PSA process containing four layers of adsorbentsis preferred, more or less than four beds and more or less than fouradsorbents could easily be used without deviating from the scope of thisinvention.

[0049]FIG. 2 shows the arrangement of four layers in an adsorbent bed ofthe PSA process, with the feed end being at the bottom of the bed. Thefourth layer is optional, but most preferred for the invention asrequired for additional contaminant(s) removal. For the purpose of thisdisclosure, the uppermost layer is that which is closest to thedischarge end of the adsorber bed. In the preferred mode of operation,four adsorbents, placed in four layers, are used in the PSA process.

[0050] Referring to FIG. 2, Layer 1 is an adsorbent for removing waterand carbon dioxide. A preferred adsorbent is alumina, though otheradsorbents with preferential selection for water and/or carbon dioxidemay be used. The amount of this adsorbent is typically less than 5% ofthe total bed volume, though this would depend upon the amount of waterand/or carbon dioxide in the feed, as well as the operating conditions(e.g. pressures) of the adsorber. The determination of the appropriateamount is well within the skill of the skilled artisan.

[0051] Layer 2 is used for removing CO, CH₄, residual CO₂, and some orall of the nitrogen. Activated carbon having a bulk density of 25-45lb/ft³ is preferred for this layer, though other adsorbents withpreferential selection for CO, CH₄, residual CO₂, and some or all of thenitrogen may be used. The amount of this adsorbent is typically on theorder of 40-70% of the total bed volume, though this would depend uponthe amount of CO, CH₄, residual CO₂, and nitrogen in the feed, as wellas the operating conditions (e.g. pressures) of the adsorber. Thedetermination of the appropriate amount is well within the skill of theskilled artisan.

[0052] Layer 3 is utilized to remove residual N₂ and some or all of theO₂ in the feed gas. Adsorbents for this layer are preferably VSA6 orhighly exchanged (>90%) CaX seolites having a silica to alumia ratio of2.0 to 2.5. Other zeolites such as LiX, H15 and 5A zeolite may also beused. The amount of this adsorbent is typically on the order of 10-40%of the total bed volume, though this would depend upon the amount ofnitrogen and oxygen in the feed, as well as the operating conditions(e.g. pressures) of the adsorber. The determination of the appropriateamount is well within the skill of the skilled artisan.

[0053] Optional layer 4 is an oxygen equilibrium selective adsorbentCo{(Me2Ac2H2maldmen} (4-PyOLi) (referred to herein as “IA-3”)) which isused for the removal or residual oxygen in the stream. The amount ofthis adsorbent is typically on the order of 5% of the total bed volume,though this would depend upon the amount of oxygen in the feed, as wellas the operating conditions (e.g. pressures) of the adsorber. Thedetermination of the appropriate amount is well within the skill of theskilled artisan.

[0054] The adsorption isotherms for the impurities above on the fouradsorbents are shown in FIGS. 3-7.

[0055] The oxygen selective adsorbents (IA-3) correspond to cobalt (II)coordination complexes comprising a cobalt (II) center and five Lewisbase donors that form chemical bonds with the cobalt (II) center. IA-3is a two component system with four Lewis base donors provided by asingle molecular entity (chelating ligand), and the fifth Lewis basedonor provided by a second entity. The two components are selected toorganize the structure and ensure that accessible binding sites existsfor reversible sorption of oxygen.

[0056] Other oxygen selective adsorbents (e.g., IC2) could be usedinstead of IA-3 in each adsorber of the PSA process. The compounddesignated as IC2, abbreviated as Co {3,5-diBu^(t)sal/(EtO)(CO₂Et)Hmal-DAP} is the cobalt (II) complex of the dianion of achelating ligand prepared formally by the 1:1 condensation ofethoxy-methylene diethylmalonate and 3,4-diamino pyridine, followed byschiff base condensation of the 3,5-di-tert-butysalicylaldehyde. Otherpreferred TEC's include Co{(Me₂Ac₂H₂malen} (4-PyOLi) andCo{Me₂Ac₂H₂maltmen} (4-PyOLi). These TECs, together with IA-3 aredescribed in commonly assigned U.S. Pat. No. 6,183,709 and in co-pendingcommonly assigned U.S. application Ser. No. 09/456,066 (Zhang et al) andSer. No. 09/725,845 (Zhang et al).

[0057] Any activated carbon having bulk density in the range of 25-45lb/ft³ could also be used in the PSA process of this invention.Furthermore, various ion-exchanged zeolites could be utilized in the PSAprocess of this invention. Examples include zeolites having silica toalumina ratio in the range of 2.0 to 2.5 and with high (e.g. >80%,preferably >90%) cation exchange content. Such zeolites include highlyexchanged CaX, Na-Y, Zn-X, Li-X, 13×, and 5A zeolites with silica toalumina ratios of 2.0-2.5.

[0058] Also, the zeolite layer/zone of each bed could be replaced withmultiple layers of different adsorbents.

[0059] For example, the zeolite layer could be substituted by acomposite adsorbent layer containing different adsorbent materialspositioned in separate zones in which temperature conditions favoradsorption performance of the particular adsorbent material underapplicable processing conditions in each zone. Further details oncomposite adsorbent layer design is given by Notaro et al., U.S. Pat.No. 5,674,311.

[0060] Table 1 shows the PSA feed gas composition when the heliumapplication unit is a metal atomization unit and a membrane unit is useddownstream of the PSA to recycle PSA waste gas back to the PSA process.TABLE 1 Typical PSA Feed and Product Gas Specifications Using a Heliumrecovery process with a metal atomization application. Feed Gas ProductGas Impurity Specification Specficiation N2 2.5 mole % <5 ppmv O2 1.0mole % <10 ppmv H2O 0.2 mole % <50 ppmv CO2 0.203 mole % <5 ppmv Helium96.04 mole % >99.999 mole %

[0061] The inventive helium recovery system using a PSA having at leastthree layers of adsorbents in each adsorber as described above,processes more feed gas per unit weight of adsorbent at a given P/Fratio (purge to feed) than other prior art PSA systems. This is becauseother prior art systems used multiple PSA units or more adsorbent bedsin the PSA (see e.g. Stoner et al and D'Amico et al cited above). Theinventive system offers superior performance to the prior art as theadsorbents used have higher differential loadings than the adsorbents(typically 5A) used in prior art systems. This is illustrated in FIGS.3-7 which compare isotherms for adsorbents used in the present inventionwith isotherms for prior art materials.

[0062] Given this efficiency, the amount of adsorbent required (e.g. thebed size factor) is reduced by a factor of 25-50% as compared to priorart processes. This reduction in bed size factor results in smaller voidvolumes. Consequently, less helium is lost during the regeneration ofthe bed, and higher helium recovery is achieved.

[0063] The preferred use of an additional layer of VSA6 or CaX zeoliteadsorbent upstream of an oxygen selective layer results in furtherenhanced helium recovery relative to activated carbon used in theaforementioned prior art helium recovery processes. This is because thehigher N₂ working capacitiy of VSA6 or CaX zeolite in the upstreamlayer, and O₂ working capacity in the downstream layer of each bed giveIA-3 and VSA6 or CaX adsorbents superior performance over the carbonbased adsorbent used in prior art PSA processes using activated carbonand 5A (H-15) for helium recovery.

[0064] The increased recovery of the PSA process results in a decreasein the amount of PSA waste gas that is recycled to the membrane andultimately back to the PSA feed. In addition, because of the reductionin the quantity of the recycle gas, the power consumption and operatingcost of the recycle compressor are reduced significantly in theinventive helium recovery process.

[0065] The invention will be further described with reference the fourbed PSA process shown in FIG. 8. The membrane unit used in the heliumrecovery process is documented extensively in the aforementioned priorart (see e.g. U.S. Pat. No. 5,632,803).

[0066]FIG. 8 shows four adsorbent beds (B1, B2, B3 and B4) andassociated valves and conduits that will be used to illustrate theenhanced PSA process performance of this invention. Referring to FIG. 8,the PSA process used in the helium recovery unit is disclosed over onecomplete PSA cycle, and the PSA valve switching and steps are given inTables 2 and 3, respectively. PV valves are positional valves thatcontrol gas flow in the conduits in a manner well known in the art.

[0067] Step 1 (AD1): Bed 1 (B1) is in the first adsorption step (AD1),while Bed 2 (B2) is undergoing countercurrent blowdown (BD), Bed 3 (B3)is undergoing Lie first equalization falling step (EQ1DN), and bed 4(B4) is undergoing the second pressure equalization rising step (EQ2UP).

[0068] Step 2 (AD2): Bed 1 is in the second adsorption step (AD2) and isalso supplying product gas to bed 4 that is undergoing the first productpressurization (PP1) step. During the same time, beds 2, 3 and 4 areundergoing purge, cocurrent depressurization and first productpressurization, respectively.

[0069] Step 3 (AD3): Bed 1 is in the third adsorption step (AD3), and isalso supplying product gas to Bed 4 that is undergoing the secondproduct pressurization (PP2) step. During the same time period, beds 2,3, and 4 are undergoing the first equalization rising step (EQ1UP),second equalization falling (EQ2DN), and second product pressurizationstep (PP2), respectively.

[0070] Step 4 (EQ1DN): Bed 1 is undergoing the first equalizationfalling step (EQ1DN), while bed 2 receives the gas from bed 1 and isundergoing the second equalization rising step (EQ2UP). Beds 3 and 4 arenow undergoing blowdown (BD) and the first adsorption step (PP1),respectively.

[0071] Step 5 (PPG): Bed 1 is undergoing cocurrent depressurization stepto provide purge gas (PPG) to bed 3, while Beds 2 and 4 are undergoingfirst product pressurization (PP1) and the second adsorption step (AD2),respectively.

[0072] Step 6 (EQ2DN): Bed 1 undergoes a second equalization fallingstep (EQ2DN) by sending low pressure equalization gas to bed 3 that isundergoing the first equalization rising (EQ1UP) step. Beds 2 and 4 areundergoing the second product pressurization (PP2) and third adsorptionstep, respectively.

[0073] Step 7 (BD): Beds 1 and 3 undergo the countercurrent blowdown(BD) and first adsorption (AD1) step, respectively. During this timeBeds 3 and 4 are undergoing bed-to-bed equalization, i.e., Beds 3 and 4are undergoing the second equalization rising (Eq2UP) and firstequalization falling (EQ1DN) steps, respectively.

[0074] Step 8 (PG): Bed 1 is now receiving purge gas (PG) from Bed 4,and Beds 2 and 3 are undergoing the second adsorption step and firstproduct pressurization (PP1) step, respectively.

[0075] Step 9 (EQ1UP): Bed 1 is undergoing the first equalization risingstep (EQ1UP) by receiving low pressure equalization gas from bed 4 thatis undergoing the second equalization falling step (EQ2DN). During thesame time, Beds 2 and 3 is undergoing the third adsorption step (AD3)and the second product pressurization (PP2), respectively.

[0076] Step 10 (EQ2UP): Bed 1 is undergoing the second equalizationrising step (EQ2UP) by receiving high pressure equalization gas from bed2 that is undergoing the first equalization falling step (EQ1DN). Duringthe same time, Beds 3 and 4 are undergoing the first adsorption (AD1)step and countercurrent blowdown step, respectively.

[0077] Step 11 (PP1) Bed 1 is receiving first product pressurization(PP1) gas from bed 3 that is also in the second adsorption step (AD2),while Bed 2 is undergoing cocurrent depressurization step to providepurge gas (PPG) to bed 4.

[0078] Step 12 (PP2) Bed 1 is receiving second product pressurization(PP2) gas from bed 3 that is also in the third adsorption step (AD3).During the same time, Bed 2 undergoes a second equalization falling step(EQ2DN) by sending low pressure equalization gas to bed 4 that isundergoing the first equalization rising (EQ1UP) step.

[0079] The valve switching logic for the four bed PSA process of FIG. 8is shown in Table 2, and the duration of each step in the PSA cycle asshown in Table 3. However, it should be noted that the twelve step PSAcycle is used only to illustrate the enhanced PSA process performanceachieved by replacing conventional carbon based adsorbents used in priorwith a layered arrangement of adsorbents to remove several kinds ofimpurities. Further, the upper layers (Layers 3 & 4) are used primarilyfor the removal of trace level of impurities, whereas, the upstreamlayers (alumina and activated carbons) are used for bulk impurityremoval. In addition, other PSA cycles may also be used to show theenhanced PSA process performance without deviating from the scope ofthis invention

[0080] Note from Tables 2 and 3 that the four beds operate in parallel,and during ¼ of the total cycle time one of the beds is in theadsorption step, while the other beds are either undergoing pressureequalization, purge, blowdown, or product pressurization. TABLE 2 FourBed H2 PSA Valve Switching (O = OPENED, C = CLOSED) Step 1 2 3 4 5 6 7 89 10 11 12 Bed 1 AD1 AD2 AD3 EQ1 PPG EQ2 BD PG EQ1 EQ2 PP1 PP2 (BD1) DNDN UP UP Bed 2 BD PG EQ1 EQ2 PP1 PP2 AD1 AD2 AD3 EQ1 PPG EQ2 (BD2) UP UPDN DN Bed 3 EQ1 PPG EQ2 BD PG EQ1 EQ2 PP1 PP2 AD1 AD2 AD3 (BD3) DN DN UPUP Bed 4 EQ2 PP1 PP2 AD1 AD2 AD3 EQ1 PPG EQ2 BD PG EQ1 (BD4) UP DN DN UPValve No. 14 O O O C C C C C C C C C 15 C C C C C C O O O C C C 16 C C CC C C C C C O O O 17 C C C O O O C C C C C C 18 O O C O O C O O C O O C19 C C C C C C O O C C C C 20 O O C C C C C C C C C C 21 C C C O O C C CC C C C 22 C C C C C C C C C O O C 23 C O O C O O C O O C O O 24 O O O CC C C C C C C C 25 C C C C C C O O O C C C 26 C C C C C C C C C O O O 27C C C O O O C C C C C C 28 C C C C O O C O O C C C 29 C O O C C C C C CC O O 30 C O O C O O C C C C C C 31 C C C C C C C O O C O O 32 C C C O CC C C C O O O 33 C C C O O O C C C O C C 34 O C C C C C O O O C C C 35 OO O C C C O C C C C C

[0081] TABLE 3 Time Interval and Step Sequence of the PSA Cycle StepTime Number Interval BED #1 BED #2 BED #3 BED #4 1  0-12 AD1 BD EQ1DNEQ2UP 2 12-30 AD2/PP1 PG PPG PP1 3 30-42 AD3/PP2 EQ1UP EQ2DN PP2 4 42-54EQ1DN EQ2UP BD AD1 5 54-72 PPG PP1 PG AD2/PP1 6 72-84 EQ2DN PP2 EQ1UPAD3/PP2 7 84-96 BD AD1 EQ2UP EQ1DN 8  96-114 PG AD2/PP1 PP1 PPG 9114-126 EQ1UP AD3/PP2 PP2 EQ2DN 10 126-138 EQ2UP EQ1DN AD1 BD 11 138-156PP1 PPG AD2/PP1 PG 12 156-168 PP2 EQ2DN AD3/PP2 EQ1UP

[0082] The data presented below illustrates the benefits of theinventive system/process. We note that while both examples are withinthe scope of the invention, the example in Table 4 illustrates a morepreferred embodiment.

[0083] Table 4 gives an example of the operating conditions and the PSAprocess performance using four layers of adsorbents (as described abovewith reference to FIG. 2) (alumina, activated carbon, zeolite, and IA-3)in each adsorber and following the four bed PSA process described abovewith reference to FIG. 8. In this non-limiting example, The first layeris alumina, the second layer is Activated carbon, the third layer isVSA6 zeolite, and the fourth layer is IA-3.

[0084] Table 5 shows an alternate embodiment of the invention case usingthree layers of adsorbents (alumina, activated carbon, and zeolite) andthe same PSA process operating conditions as used for the Example inTable 4. In comparing Tables 4& 5, a significant reduction in total bedsize factor and higher helium recovery for the case using IA-3 (Table 4)are realized relative to the case not using IA-3 (Table 5).

[0085] In the tables, the symbols have the following meaning: TPD=ton(2000 lb) per day of helium, kPa=1000 Pa=S. I. unit for pressure (1.0atm. =101.323 kPa), s=time unit in seconds. Also, in the tables, thenitrogen equilibrium selective adsorbent is VSA6, and the oxygenequilibrium selective adsorbent such as IA3. The results shown in thetables correspond to the cases where PSA waste gas, obtained during theregeneration steps of the PSA cycle, is fed to a membrane unit asdescribed above. The permeate from the membrane unit is recycle back tothe PSA feed. Thus, the PSA feed is a combination of the exhaust gasleaving the helium using application and the recycle gas from themembrane unit. Also, a hydrogen removal unit was placed at the upstreamend of the PSA process. The results shown below were obtained from PSAsimulation results using a feed mixture of: 96.037% He, 0.263% CO₂,0.20% H₂O, 1.0% O₂ and 2.5% N₂. Also, in the table, total bed sizefactor is the total quantity of adsorbents per ton per day of Heproduced. Cycle time (s) 168 Adsorbent in first layer of Bed AluminaAmount of alumina (lb/TPD He): 3.2437 × 10² Adsorbent in second layer ofbed: activated carbon Amount of activated carbon (lb/TPD He): 6.3568 ×10² Adsorbent in third layer of bed: VSA 6 Amount of VSA6 zeolite(lb/TPD He):  8.727 × 10² Adsorbent in fourth layer of bed: IA-3 Amountof IA-3 (lb/TPD He):  1.164 × 10² High Pressure:  1.312 × 10³ kPa LowPressure:  1.05 × 10² kPa Feed Flux: 2.9027 × 10⁻² kmol/s · m² HydrogenPurity: >99.999% PSA Per Pass Helium Recovery:      72% PSA/membraneHelium Recovery:    >98% Total Bed Size Factor (lb/TPD He): 1.9492 × 10³Temperature: 316 K

[0086] TABLE 5 The results shown below were obtained from PSA simulationresults using a feed mixture of: 96.037% He, 0.263% CO₂, 0.20% H₂O, 1.0%O₂ and 2.5% N₂. Also, in the table, total bed size factor is the totalquantity of adsorbents per ton per day of He produced. Cycle time (s)168 Adsorbent in first layer of Bed Alumina Amount of alumina (lb/TPDHe): 3.2437 × 10² Adsorbent in second layer of bed: activated carbonAmount of activated carbon (lb/TPD He): 6.3568 × 10² Adsorbent in thirdlayer of bed: VSA 6 Amount of VSA6 zeolite (lb/TPD He): 1.3963 × 10³Adsorbent in fourth layer of bed: None Amount of IA-3 (lb/TPD He):  0.0High Pressure:  1.312 × 10³ kPa Low Pressure:  1.05 × 10² kPa Feed Flux:2.9027 × 10⁻² kmol/s · m² Hydrogen Purity: >99.999% PSA Per Pass HeliumRecovery:      60% PSA/membrane Helium Recovery:    >95% Total Bed SizeFactor (lb/TPD He): 2.3564 × 10³ Temperature: 316 K

[0087] An alternative embodiment will be described with reference toFIG. 9.

[0088] Helium gas (typically having a purity of 99.999 mole %) issupplied to an Application 6 from a product ballast tank 8 via conduit 8a. At start-up gas is supplied to ballast tank 8 via conduit 9 b fromsource 9. The Application will introduce varying amounts of streamimpurities into the helium. This contaminated helium (e.g. having apurity of 99%) is removed from the Application as a “used” gas stream.The used gas directed through an optional hydrogen removal system, ifnecessary (this hydrogen removal system is illustrated in FIG. 1). Thegas is then collected by the PSA feed compressor 4 and recycled to therecovery system (including at least PSA 6) via conduit 4 a for clean-upbefore being forwarded to the product ballast tank 8 for re-use. Some ofthe used gas reclaimed from the Application is too rich in impuritiesfor the recycle system to handle, it must therefor be vented as wastevia conduit 100 rather than recycled. The gas lost in this venting stepis replaced with helium from a source 9 via conduit 9 a. Periodicallythe PSA adsorbent beds will need to be regenerated. This regenerationprocess creates a helium-rich waste stream.

[0089] To effect greater recovery, the PSA waste stream is recycled viaconduit 6 b and optional surge tank 10, directly back to the PSA feedcompressor 4 via line 500 when the impurity level is low. Recycling thePSA waste gas causes the impurity concentrations in this recycle streamto accumulate over successive cycles. At some point these impuritieswill reach a concentration that will exceed the capacity of the PSAadsorber vessels. An analyzer monitors the waste stream for this upperlimit at position A in FIG. 9. When this upper setpoint is reached themajority of the PSA waste gas stream is redirected via line 10 a tocompressor 200, then to the membrane 7. The membrane quickly rejects PSAwaste stream impurities via line 300, enriching the recycled wastestream 400 in helium. When the analyzer at position A indicates that thelower impurity setpoint has been reached membrane compressor capacity isreduced and the majority of the PSA waste gas stream is again directedvia line 500 and other conduits to the suction side of the PSA feedcompressor 4.

[0090] The system keeps pace with the Application demand by monitoringthe PSA feed compressor suction pressure at position B. High Applicationusage rates lead to higher amounts of used helium at the PSA compressorinlet. This results in a higher inlet pressure. The higher inletpressure will cause the compressor to increase capacity in an effort toreduce the inlet pressure. This generates additional helium for theApplication. Falling suction pressure serves to decrease the compressorcapacity, thus having the opposite effect on available helium product.If increasing the compressor throughput does not provide sufficienthelium to maintain the ballast tank delivery pressure setpoint, thesystem will automatically add make-up gas (from source 9) to the PSAfeed compressor inlet via line 9 a. The addition of gas will serve toincrease the inlet pressure further, thus causing the compressor toincrease its capacity further, making additional product available tothe ballast tank. System integrity is ensured by monitoring the productpurity through an analyzer located at position C in FIG. 1.

[0091] The inventive recovery system is capable of processingcontaminated helium gas streams from one or more applications. Forexample, one recovery process can operate with one or more furnaces.However, for maximum reliability the recovery system can have enindependent recovery system for each application with cross ties betweenthe systems as shown in FIG. 10. The membrane unit(s) 7′ and 7″ may notbe necessary when the PSA per pass recovery is high (>90%). However,whenever the recovery from the PSA process is considered too low (e.g.,less than 90%), then the use of a membrane unit is preferred to conservemore than 90% of the gase (e.g., helium).

[0092] The helium recovery system shown in FIG. 10 has the flexibilityof using one PSA system for each application with cross ties to allowany application to use any PSA. Note that because the reference numbersrefer to similar components as in FIGS. 1 and 9, they are identified as1′ and 1″ (e.g. for the application).

[0093] The recovery processes for each application/recovery systemoperate in essentially the same manner as in FIGS. 1 and/or 9, with thedifference being that a specific application (1′ or 1″) is not requiredto operate in conjunction with a specific recovery system (e.g. specificPSA and/or specific membrane).

[0094] The applications 1′ and 1″ can operate either under positive orsubambient pressure. The off-gas from each application 1, 1″ would passvia conduits 1 a′ and 1 a″ through a vacuum pump 3′, 3″ (if undersubambient pressure) via conduits 3 a′ and 3 a″, and one or more ofcontrol valves 32′, 32′″ via one or more conduits 32 a to the suctionside of a compressor 4′, 4″ and/or 4′″. The compressor would have aby-pass loop such that as the number of applications decreased theby-pass valves (e.g. (e.g. 32′, 32″, 33′, 33″, 33″′, 34′, 34″ and 35′,35″)for the compressor would open to maintain a constant compressordischarge.

[0095] Thus if only application 1′ were used and only compressor 4′ wereused, valves 32′ 32″ would be closed and 35′ would be opened. Further,depending upon which PSA unit (6′ or 6″) were to be used, one or more ofvalves 34′ or 34″ would be opened to allow for gas flow through conduits33 a′, 33 a″, 34 a″ or 33 a′″ depending upon the desired recyclingprocess loop.

[0096] The gas is passed from the recycle compressor(s) (4′, 4′″, 4′″)to one or more of the optional hydrogen removal systems 5′ and 5″, ifnecessary, and one or more of the the PSA purifiers 6′ and 6″ asdescribed above. Purified helium gas is returned via conduits 6 a′and/or 6 a″, ballast tanks 8′ and/or 8″ and conduits 8 a′ and/or 8 a″ tothe applications 1′ and/or 1″. Waste gas is partially vented viaconduits 11′ and 11″ (if applicable), with the balance passing via lines6 b′ and/or 6 b″ through optional surge tanks 10′ and 10″ to optionalmembrane units 7′ and 7″ if applicable. Helium depleted raffinate isremoved from the membrane via conduits 300′ and/or 300″. Helium enrichedgas from the membrane is recycled via lines 400′ and/or 400″ through oneor more of compressors 4′, 4″ and/or 4′″ back to the adsorption unit(6′, 6″).

[0097] We note that supply 9″ may be used as a source of the originalfeed gas for the application (via lines 9 b′ and/or 9 b″ and openedvalve 37) in the same manner as in FIGS. 1 and/or 9; and or as make-upgas to replace gas lost in the process (e.g. through venting) via lines9 a″ in a similar manner as in FIGS. 1 and/or 9.

[0098] Although the above PSA process is discussed in relation to heliumrecovery, the aforementioned key features could also be extended toother separation processes, e.g. noble gas revovery, H2 and CO₂production from synthesis gas or other sources containing H2 and CO₂ inthe feed, or in other PSA processes for co-production of H₂ and CO.

[0099] The novel helium recovery process is capable of removing aircontaminants, hydrogen and particulate from various applications. Therecovery system is unique because hydrogen in the recycle stream is keptto a minimum by operating the catalyst bed in the hydrogen removal unitwith excess oxygen.

[0100] Additional unit operations may hp included in the recovery unitwere it is necessary to remove other contaminants, e.g., metals, andmetal salts from spent/used helium exiting from some applications, e.g.,an atomization furnace that produce powders. Such operations (e.g. theuse of bag housings or filters) are well known to those skilled in theart.

[0101] Also, in prior art hybrid processes (e.g., PSA & membrane),recycling of the waste gas stream from the PSA to the membrane occursintermittently based on the composition of the waste gas obtained duringthe regeneration of the PSA beds. However in the present invention (withreference to FIGS. 1 and/or 9), a fraction of the helium entering thesurge tank 10 (upstream of the membrane and downstream of the PSA wasteend) may be vented continuously to balance the amount of impurities inthe total system with the impurities coming from the helium application.Since the waste gas from the PSA 6 goes through the surge tank 10, thenthe membrane 7, then back to The suction side of the recycle compressor4; the PSA will concentrate the impurities from 10 to 10,000 timesgreater than what is coming from the application 1. Thus, the amount ofhelium discarded via lines 11, 12 can be relatively small, and highhelium recovery (e.g. greater than 90 to 95%) is achieved.

[0102] Although the invention has been described with reference tospecific embodiments as examples, it will be appreciated that it isintended to cover all modifications and equivalents.

[0103] The term “comprising” is used herein as meaning “including butnot limited to”, that is, as specifying the presence of stated features,integers, steps or components as referred to in the claims, but notprecluding the presence or addition of one or more other features,integers, steps, components, or groups thereof.

[0104] Specific features of the invention are shown in one or more ofthe drawings for convenience only, as each feature may be combined withother features in accordance with the invention. Alternative embodimentswill be recognized by those skilled in the art and are intended to beincluded within the scope of the claims.

1. A gas recovery system comprising a source of gas having a preselectedconcentration of a desired component (9), at least one application (1)that adds impurities to said gas, and at least an adsorption system (6)that purifies said gas to produce a purified gas for re-use inapplication (1), wherein said at least one adsorption system includes atleast one adsorbent bed (A) having at least three layers of adsorbents.2. The gas recovery system of claim 1, wherein the first layer ofadsorbent comprises an adsorbent selective for one or more of water andcarbon dioxide, the second layer of adsorbent comprises an adsorbentselective for one or more of CO, CH₄, carbon dioxide and nitrogen, andthe third layer of adsorbent comprises an adsorbent selective for one ormore of nitrogen and oxygen.
 3. The gas recovery system of claim 2,wherein said adsorbent bed further comprises a layer of an oxygenselective adsorbent.
 4. The gas recovery system of any one of claims1-3, wherein said first adsorbent layer comprises alumina, said secondadsorbent layer comprises activated carbon and said third adsorbentlayer comprises a zeolite.
 5. The gas recovery system of claim 3,wherein said oxygen selective adsorbent is IA-3.
 6. The gas recoverysystem of claim 4, wherein said zeolite is selected from the groupconsisting of VSA6, CaX zeolite having greater than 90% Ca exchange,LiX, H-15 and 5A.
 7. The gas recovery system of claim 4, wherein saidactivated carbon has a bulk density of 25 pounds/foot³ to 45pounds/foot³.
 8. The gas recovery system of claims 1, wherein saidsystem further comprises at least one membrane (7) for purifying a wastestream containing the desired component that is produced from said atleast one adsorption system (6).
 9. The gas recovery system of claims 1,wherein said at least one adsorption system (6) includes four adsorbentbeds (A-D).
 10. The gas recovery system of claims 1, wherein saiddesired component is selected from the group consisting of the noblegases.
 11. The gas recovery system of claims 1, wherein said desiredcomponent is helium, and said preselected concentration is 99.999 mole%.
 12. A gas recovery process comprising the steps of a) providing gashaving a preselected concentration of a desired component to anapplication (1), b) adding impurities to said gas in said application(1) to produce an impure gas having a lower concentration of saiddesired component; c) passing said impure gas to an adsorption system(6) that purifies said gas to produce a purified gas having saidpreselected concentration of said desired component for re-use inapplication (1), wherein said adsorption system includes at least oneadsorbent bed (A) having at least three layers of adsorbents.
 13. Thegas recovery process of claim 12, wherein said adsorption systemproduces a waste gas having a second concentration of said desiredcomponent which is lower than said preselected concentration, andwherein said waste gas is recirculated through said adsorption systemfor purification, and wherein said purified recirculated gas is providedto said application.
 14. The process of any one of claims 12-13, whereinsaid adsorption system produces a waste gas containing said desiredcomponent, and wherein said waste gas is directed to a membrane system(7) which produces a partially purified gas having a higherconcentration of said desired component than said waste gas, and whereinsaid partially purified gas is combined with said impure gas prior whichis then passed through said adsorption system for purification.
 15. Theprocess of any one of claims 12, wherein said desired component ishelium.
 16. The process of any one of claims 12, wherein said adsorptionsystem (6) comprises four beds (A-D).
 17. The process of any one ofclaims 12, wherein the first layer of adsorbent comprises an adsorbentselective for one or more of water and carbon dioxide, the second layerof adsorbent comprises an adsorbent selective for one or more of CO,CH₄, carbon dioxide and nitrogen, and the third layer of adsorbentcomprises an adsorbent selective for one or more of nitrogen and oxygen.18. The process of any one of claims 12, wherein said adsorbent bedfurther comprises an oxygen selective adsorbent.
 19. The process of anyone of claims 12, wherein said first adsorbent layer comprises alumina,said second adsorbent layer comprises activated carbon and said thirdadsorbent layer comprises a zeolite.
 20. The process of claim 18,wherein said oxygen selective adsorbent is IA-3.
 21. The process ofclaim 19, wherein said zeolite is selected from the group consisting ofVSA6, CaX zeolite having greater than 90% Ca exchange, LiX, H-15 and 5A.22. The process of claim 19, wherein said activated carbon has a bulkdensity of 25 pounds/foot³ to 45 pounds/foot³.